1. Technical Field
This disclosure relates to methods of preparing polypropylene films. More specifically, this disclosure relates to multi-layer polypropylene films for use in thermo-lamination applications and methods of making and using same.
2. Background
Synthetic polymeric materials, particularly polypropylene resins, are manufactured into a variety of end-use articles ranging from medical devices to materials packaging. Many industries, such as the packaging industry, utilize these polypropylene materials in various manufacturing processes to create a variety of finished goods including containers, packaging films for food packaging, thermo-lamination films for book covers, etc. For example, producing thermo-lamination films may involve extruding a layer of ethylene vinyl acetate (EVA) onto a plastic film (e.g., polypropylene) to form a bilayer film. Next, the EVA side of the bilayer film may be thermo-laminated to different types of substrates (e.g., paper, wood, etc.) to form polypropylene-EVA laminates.
One challenge to the utility of polypropylene-EVA laminates is achieving sufficient bond strength between the polypropylene film and the EVA layer. In order to improve the bonding between these layers, a tie layer may be placed between the polypropylene film and the EVA layer. However, adding a tie layer increases the cost associated with producing such materials and may detrimentally affect one of more physical properties (e.g., low haze, high gloss) of the material. Thus an ongoing need exists for novel laminate compositions having desirable physical and/or mechanical properties.